Remove explicit width suffixes from Arm bignum assembly
Remove explicit width suffixes from Arm bignum assembly

Within the M-profile of the Arm architecture, some instructions
admit both a 16-bit and a 32-bit encoding. For those instructions,
some assemblers support the use of the .n (narrow) and .w (wide)
suffixes to force a choice of instruction encoding width.
Forcing the size of encodings may be useful to ensure alignment
of code, which can have a significant performance impact on some
microarchitectures.

It is for this reason that a previous commit introduced explicit
.w suffixes into what was believed to be M-profile only assembly
in library/bn_mul.h.

This change, however, introduced two issues:
- First, the assembly block in question is used also for Armv7-A
  systems, on which the .n/.w distinction is not meaningful
  (all instructions are 32-bit).
- Second, compiler support for .n/.w suffixes appears patchy,
  leading to compilation failures even when building for M-profile
  targets.

This commit removes the .w annotations in order to restore working
code, deferring controlled re-introduction for the sake of performance.

Fixes #6089.

Signed-off-by: Hanno Becker <4d488caff78d6184f59bbe6e137e34d4606b9fe8@arm.com>

Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls